Sorry, I picked you up wrong, my fault.
1. Yes, you would replace the header graphic with your own if the one provided is not suitable.
2. You would not create or replace your own sample text. If you do this then you are restricted to the pages provided with the template. If I were you I would modify the template to suit your needs then create the new pages you require from this.
(Regarding copyright, be careful if you are using any of the images and graphics supplied with the template. Ensure that there is no copyright on the images or it may come back to bite you later. There are thousands of instances on the net where free template providers have supplied their wares with copyrighted images and users have been pursued for this when caught using them online.)